diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/GenerateRowConcat.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/GenerateRowConcat.scala
index 16eb4cbcf8188..c7e06bb961e8c 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/GenerateRowConcat.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/GenerateRowConcat.scala
@@ -58,7 +58,7 @@ object GenerateRowConcat extends CodeGenerator[(StructType, StructType), UnsafeR
     // The only reduction comes from merging the bitset portion of the two rows, saving 1 word.
     val sizeReduction = bitset1Words + bitset2Words - outputBitsetWords
 
-    // Copy bitset from row1: pretty straightforward
+    // --------------------- copy bitset from row 1 ----------------------- //
     val copyBitset1 = Seq.tabulate(bitset1Words) { i =>
       s"""
          |PlatformDependent.UNSAFE.putLong(buf, ${offset + i * 8},
@@ -66,6 +66,8 @@ object GenerateRowConcat extends CodeGenerator[(StructType, StructType), UnsafeR
        """.stripMargin
     }.mkString
 
+
+    // --------------------- copy bitset from row 2 ----------------------- //
     var copyBitset2 = ""
     if (bitset1Remainder == 0) {
       copyBitset2 += Seq.tabulate(bitset2Words) { i =>
@@ -75,8 +77,6 @@ object GenerateRowConcat extends CodeGenerator[(StructType, StructType), UnsafeR
          """.stripMargin
       }.mkString
     } else {
-      // Copy bitset from row2: slightly more complicated here, as we need to use the leftover
-      // space from the first bitset.
       copyBitset2 = Seq.tabulate(bitset2Words) { i =>
         s"""
            |long bs2w$i = PlatformDependent.UNSAFE.getLong(obj2, ${offset + i * 8});
@@ -105,7 +105,8 @@ object GenerateRowConcat extends CodeGenerator[(StructType, StructType), UnsafeR
         }
       }.mkString("\n")
 
-      if (bitset2Remainder > (64 - bitset1Remainder)) {
+      if (bitset2Words > 0 &&
+        (bitset2Remainder == 0 || bitset2Remainder > (64 - bitset1Remainder))) {
         val lastWord = bitset2Words - 1
         copyBitset2 +=
           s"""
@@ -115,6 +116,38 @@ object GenerateRowConcat extends CodeGenerator[(StructType, StructType), UnsafeR
       }
     }
 
+    // --------------------- copy fixed length portion from row 1 ----------------------- //
+    val copyFixedLengthRow1 = s"""
+       |PlatformDependent.UNSAFE.copyMemory(
+       |  obj1, offset1 + ${bitset1Words * 8},
+       |  buf, offset + ${outputBitsetWords * 8},
+       |  ${schema1.size * 8});
+     """.stripMargin
+
+    // --------------------- copy fixed length portion from row 2 ----------------------- //
+    val copyFixedLengthRow2 = s"""
+       |PlatformDependent.UNSAFE.copyMemory(
+       |  obj2, offset2 + ${bitset1Words * 8},
+       |  buf, offset + ${(outputBitsetWords + schema1.size) * 8},
+       |  ${schema2.size * 8});
+     """.stripMargin
+
+    // --------------------- copy variable length portion from row 1 ----------------------- //
+    val copyVariableLengthRow1 = s"""
+       |PlatformDependent.UNSAFE.copyMemory(
+       |  obj1, offset1 + ${(bitset1Words + schema1.size) * 8},
+       |  buf, offset + ${(outputBitsetWords + schema1.size + schema2.size) * 8},
+       |  row1.getSizeInBytes() - ${(bitset1Words + schema1.size) * 8});
+     """.stripMargin
+
+    // --------------------- copy variable length portion from row 2 ----------------------- //
+    val copyVariableLengthRow2 = s"""
+       |PlatformDependent.UNSAFE.copyMemory(
+       |  obj1, offset1 + ${(outputBitsetWords + schema1.size + schema2.size) * 8},
+       |  buf, offset + ${(outputBitsetWords + schema1.size + schema2.size) * 8},
+       |  ${schema1.size * 8});
+     """.stripMargin
+
 
     val code = s"""
        |public Object generate($exprType[] exprs) {
@@ -151,6 +184,8 @@ object GenerateRowConcat extends CodeGenerator[(StructType, StructType), UnsafeR
 
     logDebug(s"code for GenerateRowConcat($schema1, $schema2):\n${CodeFormatter.format(code)}")
 
+    // println(CodeFormatter.format(code))
+
     val c = compile(code)
     c.generate(Array.empty).asInstanceOf[UnsafeRowConcat]
   }
diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/codegen/GenerateRowConcatSuite.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/codegen/GenerateRowConcatSuite.scala
index 591c5763fe1d7..b2f681c0fcaeb 100644
--- a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/codegen/GenerateRowConcatSuite.scala
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/codegen/GenerateRowConcatSuite.scala
@@ -37,6 +37,12 @@ class GenerateRowConcatSuite extends SparkFunSuite {
   }
 
   private def testBitsets(numFields1: Int, numFields2: Int): Unit = {
+    for (i <- 0 until 5) {
+      testBitsetsOnce(numFields1, numFields2)
+    }
+  }
+
+  private def testBitsetsOnce(numFields1: Int, numFields2: Int): Unit = {
     val schema1 = StructType(Seq.tabulate(numFields1) { i => StructField(s"a_$i", IntegerType) })
     val schema2 = StructType(Seq.tabulate(numFields2) { i => StructField(s"b_$i", IntegerType) })
 
@@ -64,8 +70,8 @@ class GenerateRowConcatSuite extends SparkFunSuite {
 
       s"""
          |input1: ${set1.mkString}
-          |input2: ${set2.mkString}
-          |output: ${out.mkString}
+         |input2: ${set2.mkString}
+         |output: ${out.mkString}
        """.stripMargin
     }
 
@@ -78,62 +84,63 @@ class GenerateRowConcatSuite extends SparkFunSuite {
     }
   }
 
-  test("boundary size 0, 0") {
+  test("bitset concat: boundary size 0, 0") {
     testBitsets(0, 0)
   }
 
-  test("boundary size 0, 64") {
+  test("bitset concat: boundary size 0, 64") {
     testBitsets(0, 64)
   }
 
-  test("boundary size 64, 0") {
+  test("bitset concat: boundary size 64, 0") {
     testBitsets(64, 0)
   }
 
-  test("boundary size 64, 64") {
+  test("bitset concat: boundary size 64, 64") {
     testBitsets(64, 64)
   }
 
-  test("boundary size 0, 128") {
+  test("bitset concat: boundary size 0, 128") {
     testBitsets(0, 128)
   }
 
-  test("boundary size 128, 0") {
+  test("bitset concat: boundary size 128, 0") {
     testBitsets(128, 0)
   }
 
-  test("boundary size 128, 128") {
+  test("bitset concat: boundary size 128, 128") {
     testBitsets(128, 128)
   }
 
-  test("single word bitsets") {
+  test("bitset concat: single word bitsets") {
     testBitsets(10, 5)
   }
 
-  test("first bitset larger than a word") {
+  test("bitset concat: first bitset larger than a word") {
     testBitsets(67, 5)
   }
 
-  test("second bitset larger than a word") {
+  test("bitset concat: second bitset larger than a word") {
     testBitsets(6, 67)
   }
 
-  test("no reduction in bitset size") {
+  test("bitset concat: no reduction in bitset size") {
     testBitsets(33, 34)
   }
 
-  test("two words") {
+  test("bitset concat: two words") {
     testBitsets(120, 95)
   }
 
-  test("bitset 595, 960") {
+  test("bitset concat: bitset 65, 128") {
     testBitsets(65, 128)
   }
 
-  test("randomized tests") {
+  test("bitset concat: randomized tests") {
     for (i <- 1 until 20) {
       val numFields1 = Random.nextInt(1000)
       val numFields2 = Random.nextInt(1000)
+      info(s"num fields: $numFields1 and $numFields2")
       testBitsets(numFields1, numFields2)
     }
   }